The pull-request https://github.com/CGAL/cgal/pull/3413 has introduced
a side-effect: CTest was broken when `CGAL_HEADER_ONLY=OFF`, for all
tests using a `.cin` or `.cmd` file. That is due to the variable
`CGAL_CURRENT_SOURCE_DIR` that was only filled by `UseCGAL.cmake`.
Now that we forbid CGAL directories without `CMakeLists.txt`, that
variable `CGAL_CURRENT_SOURCE_DIR` is now useless, and can be removed:
`CMAKE_CURRENT_SOURCE_DIR` is sufficient. That fixes the bug with
CTest, and also makes the CMake code a bit simpler.
- split `cgal_add_test()` into `cgal_add_test()` and
`cgal_add_compilation_test()`
- `cgal_add_test()` have more parameters:
- an optional custom `TEST_NAME`,
- extra arguments to use for the test.
- Add CTest support for `test/Sweep_line_2/`